Centrally loaded inductively tunable whip antenna



Dec. 28, 1965 R. Rn'cHlE ETAL GENTRALLY LOADED INDUCTIVELY TUNABLE WHIP ANTENNA Filed Feb. 27, 1962 J R [lll/een f I tlarneys Inventors ?A Pfff/11 United States Patent Ofice 3,225,725 Patented Dec. 28, i965 3,226,725 CENTRALLY LAED INDUCTIVELY TUNABLE WHP ANTENNA Roy Ritchie and Sohn R. Killeen, Cambridge, Engiand, assignors to Pye Limited, Cambridge, England, a British company Filed Feb. 27, 1962, Ser. No. 175,997 Claims priority, application Great Britain, Mar. l, 1961, 7,464/6ll 13 Claims. (Cl. 343-745) The present invention relates to H. F. aerials, and more particularly to aerials suitable for use with mobile equipment at frequencies which are low enough to preclude the use of resonant length aerials in such mobile equipment. that is loaded to give resonance at the desired frequency. This may be achieved by inserting a coil between the feeder and the whip, and this is termed bottom-loading. Such an arrangement means that the coil is in a high current region and its inductance is therefore most effective and only a small coil is needed, but such a coil will only contribute a little to the radiation of signals from the aerial system and moreover a very high Q coil is required in order to minimise the insertion loss. If a coil is inserted at some point along the length of the aerial, i.e., the aerial is centre-load, then a larger coil is required, but it can appreciably increase the radiation eiiiciency with a Q of much lower order than would be required for a bottom loading coil. However, the insertion of a coil at an intermediate point on the whip introduces both electrical and mechanical problems. The assembly must be strong, but also ilexible and weatherproof, and whilst it may not be diiiicult to achieve this when a single frequency aerial is required, when an aerial is required which can work over a fairly broad band of frequencies, as is usually the case, then tuning by adjustment of the coil located at an intermediate point on the aerial is most difficult to achieve. This has led to the prevalent use of bottom-loaded aerials where the coil can be contained within a casing at the base of the aerial.

The present invention provides a centre-loaded whip aerial with a coil that may be adjusted to give a frequency range of 7 or 8:1. Say between 2 to l5 mc./s. for example.

The present invention consists in a tunable whip aerial wherein one end of the whip is connected to a iiexible housing of insulating material containing at least one coil having one end electrically connected to the whip and which contributes substantially to the radiation efficiency of the aerial, means being provided for adjusting the inductance value of said coil so as to effect tuning of the aerial and a radiating member within the housing and extending from the other end of the coil to that connected to the whip so that the aerial is effectively centre-loaded.

According to one embodiment of the invention, the whip is connected to a exibie tubular housing of insulating material containing an inner rotatable externally threaded member on which is mounted a nut member xe-d against rotation relative to the housing but which is slidable relative thereto so that it travels along the threaded member when said member is rotated. An electrical conductor has one end electrically connected to the whip and is wound about said threaded member to form a coil the turns of which are located in at least some of the grooves of the threaded member, the other end of said conductor passing through an aperture in the nut member and extending down the remainder of the housing. Preferably means are provided for tensioning this latter portion of the conductor and for connecting a feeder thereto. Driving means are also provided for rotating the inner Such aerials normally comprise a whip aerial` threaded member and thereby varying the number of turns of the conductor wound as a coil round said member.

In an alternative embodiment two spaced nut members are provided on the threaded member and two portions of the conductor are wound about said threaded member to form two coils respectively situated on the sides of the nut members which are remote from each other. With this arrangement as the threaded member is rotated the turns of one coil will be decreased as the turns of the other coil are increased. At least a portion of the threaded member is hollow to accommodate a ferromagnetic core and at least another portion constitutes a paramagnetic core and/ or a diamagnetic core, so that variation of the type of core within each coil increases the change of inductance effected as the turns are transferred from one coil to the other with rotation of the threaded member. In this embodiment the other end of the conductor may be secured to a conducting member forming part of or attached to the threaded member and also constituting a section of the aerial.

According to another embodiment of the invention the ilexible housing of insulating material contains a fixed coil within which is located an inner member forming a composite tuning core having a section of ferromagnetic material, a section of non-conducting paramagnetic or diamagnetic material and a section of electrically conducting paramagnetic or diamagnetic material, this tuning core being movable relative to the coil in order to alter the inductance thereof and thereby tune the aerial.

In order that the invention may be more fully understood reference will now be made to the accompanying drawings, in which:

FIGURE 1 is a somewhat diagrammatic view partly in section of one embodiment of whip aerial according to this invention,

FIGURE 2 is a similar view of another embodiment, and

FIGURE 3 is a similar view of a third embodiment.

Referring now to FIGURE 1, a metal whip aerial member, a portion of which is shown at i, and which may be approximately a quarter wavelength long at the highest frequency in the band, is mounted on a exible tube 2 of Fibreglas, or other suitable insulating material, the junction 3 between the whip l and tube 2 being weatherproof. Within the tube 2 is located an externally threaded ilexible Fibreglas inner tube or rod 4, which is mounted in bearings 5 and 6 at each end so that it is free to rotate. The bearing 6 is formed in a cover plate 7 attached to the lower end of tube Z. A nut member 8, of nylon or other suitable insulating material is engaged on the thread of the inner member 4 and the nut has a projection 8a that engages with a straight slot or groove in the inner surface of the wall of the tube 2, so that the nut cannot rotate but is free to slide up or down within the outer tube Z when the threaded member 4 is rotated. A rotatable electrical connection is provided between the whip aerial 1 and a bare conductor 9 xed to the top end of the inner member 4, this is shown as a slip ring 16 and brush il, but could be a ball bearing connection on the axis of the inner member, for example. The conductor is then laid in a spiral around the inner member 4, along the screw thread, which may for example have llt? turns per inch, to form a coil 16. At the nut member 8, the conductor 9 passes through a hole in the nut, and then lies parallel to the inner member, and is pulled under tension on to a take-up drum 12 at the base of the assembly, the turns of the conductor being shorted together. The portion of the conductor below the coil constitutes the lower section of the aerial, and a feed connection is made by a sliding Contact at the base, which may conveniently take the form of a metal pulley-wheel 13 engaging with the outer surface of the bare conductor 9. Driving means 14 are provided to rotate the threaded member 4 and hence adjust the tuning of the aerial by altering the inductance of the coil 11, andnmay comprise a bowden cable drive or a bevel gear assembly.

When the inner member 4 is rotated in one direction, the nut member t; will move up the inner member, so taking turns off the coil 1l and reducing its inductance. The4 slack in the conductor is taken up by the drum. When the inner member is rotated in the other direction the nut member S moves down the inner member, and additional turns are formed on the coil, so increasing the inductance. The nylon nut member 8 preferably has a metal eyelet 15 in the hole for the conductor to reduce static noise and friction between the bare conductor 9 and the surface of the nut member.

A typical embodiment of aerial tunable over the frequencies between 2 and 15 mc./s. would have a 4 ft. loaded section within the housing 2. The inner member 4 would be of 1A diameter, and the conductor 9 would be 25 ft. long, with a capacity on the take-up drum l2 of 21 ft.

The aerial only requires a matching transformer, and the tuning may be metered by the use of a current transformer consisting of a ferrite cored toroid about the live conductor or feeder. The output from this toroid is recit-led and smoothed and may be used to give a visual indication on a meter or to drive a servo system and so adjust the y inductance.

The assembly is compact, robust and weatherproof, and has the advantage of centre-loading in that the coil 11 contributes substantially to the radiation efficiency of the aerial.

Another embodiment is shown in FIGURE 2. The metal whip aerial member 1 is attached to a tubular flexible housing Z of insulating material which contains two nylon nut members 2S associated with a flexible threaded inner member 24. At least the upper section of the inner member 24 is hollow, and contains a ferromagnetic core 25. For the frequency range hereinbefore mentioned the core will be approximately 8 in length, and is preferably composed of a plurality of separate short lengths arranged in abutting relationship. Eight units l long have been used, v.and the effect on the inductance of splitting the core into short lengths is found to beY negligible as the ends are smooth, while the danger of fracture is reduced and the core may actually flex with the housing 2 if necessary. Resilient pads 26 are preferably fitted to hold the core elements firmly together. The inner member 2d has a diameter between and 1/2, and the external thread has between and 2O turns per inch. After passing through the first nylon nut member, the conductor 29 (which may be an insulated conductor in this embodiment) is laid parallel to the inner member and then passed through the second nylon nut member. The spacing between the nut members 23 must be such that the distance from the upper surface of one nut member to the lower surface of the other is at least the same length as the ferromagnetic core 25. After passing through the second nut member, the conductor is wound around the inner member 24 and its lower end firmly secured to a metal conductor 3d. This latter conductor may conveniently be formed by externally metallising the lower section of the inner member Z4. At the base of the assembly there is a sliding or rotating contact 3l. for the feeder. The overall dimensions of the aerial may be of the order of 6 feet for the Whip, and 6 feet for the tube assembly. In the tube, the first 8 comprises the loaded coil 31, then a space of 8" between the nuts, and then 8 for the lower coil 32, the final or lower 4 feet being metallised as at 3@ and forming the lower section of the aerial. The 8 region in which the lower coil 32 is formed is preferably provided with an electrically conducting ferromagnetic or diamagnetic core 34, which may be a separate core of aluminium or brass, or may be conveniently formed by an extension of the metallising Si). Between the ferromagnetic core 25 and this lower core 34 is a non-conducting paramagnetic or diamagnetic core portion 33. Means may be lifted to maintain the tension in the conductor, and one form could comprise a Phosphor-bronze spring applying a sideways thrust between the conductor and the inner member at a point between the two nuts. An alternative form would comprise forming the inner member in two portions, the break occurring at a point between the two nuts, and the upper portion being fitted on the lower portion in such a way that it cannot rotate with respect to the lower portion, but can slide towards or away from the lower portion, and a spring is fitted between the portions which will urge the two apart. With such a construction it is necessary to have means to accommodate the change in length of the inner member if the conductor should stretch.

With this arrangement, rotation of the inner member 24 causes turns to be removed from one coil and added to the other, the different core material enhancing the inductance change and as the coil section is of reduced length, the radiating efficiency is further improved.

A further embodiment of the invention is shown in FIGURE 3, and again comprises a metal whip aerial member l. attached to a tubular fiexible housing 2 of insulating material, such as Fibreglas. A conductor 40 is formed on or within the wall of the housing 2 and comprises a copper tape which extends from a conducting connecting ring il to the whip ll, down the housing to a point where it is wound into a coil 42 and then down to the lower end of the housing where it is connected to a terminal ring 43 to which an aerial feeder may be connected. Within the bore of the housing is located a core assembly 44 having an upper portion of electrically connecting paramagnetic or diamagnetic material which consists of alurninum segments 45 separated from each other by polystyrene spacers 46. The lower portion of the core is made of ferromagnetic material and consists of a plurality of separate ferrite pieces 47 arranged in abutting relationship. The upper and lower core portions are separated by a central portion of paramagnetic or diamagnetic insulating material 48. The core portions may be mounted on a flexible plastic rod or mandrel 49 which is anchored at its two ends to two members S0, Si. A control cable Si. is also attached to the lower end member 5l and can move the core assembly 44 relative to the coil 42. in order to alter its inductance. The core assembly moves against the action of a compression spring S3 contained in the housing between the lower end member 51 and the bottoni of the housing. The movement of the core assembly de under the action of the control cable 52 effectively alters the tuning of the Whip aerial. The lower end of the aerial is supported on a mounting member 54 and the housing may be filled with silicon oil and alumina filler to increase the thermal conductivity. This embodiment possesses the advantage that the turns of the coil are fixed and it does not require any rotating parts or displacement of the turns of the coil.

Whilst particular embodiments have been described it will be understood that various modifications may be made without departing from the scope of this invention. Thus the aerial may obviously be designed to operate over other frequency ranges besides those specifically described.

We claim:

l. A centredoaded tuna le Whip aerial, comprising a flexible housing of insulating material forming the base section of the aerial, a flexible metal Whip constituting a radiating member and rigidly secured to the upper end of said housing, a coil enclosed by the housing located away from the lower end of the housing and having its upper end electrically connected to said whip, a further radiating member connected to the lower end of said coil, said further radiating member being entirely enclosed by the housing and extending below said coil, and adjusting means located in said housing and operable remotely from said aerial for adjusting the inductance value of said coil so as to effect tuning of the aerial.

2. An aerial as claimed in claim 1, comprising, within the exible housing, an inner rotatable externally threaded member, a nut member mounted on said externally threaded member, said nut member being xed against rotation relative to the housing but being slidably relative thereto so that it travels along the threaded member when said member is rotated, an electrical conductor having one end electrically connected to the whip wound about said threaded member to form a coil, the turns of which are located in at least some of the grooves of the threaded member, the other end of said conductor passing through an aperture in the nut member and extending through the remainder of the interior of the housing to form said further radiating member, and means for tensioning the conductor.

3. An aerial as claimed in claim 2, in which the lower end of the conductor is fed on to a take-up drum which takes up any slack in the conductor.

4. An aerial as claimed in claim 3, including a feeder connection to the aerial in the form of a metal pulley which engages with the bare surface of the conductor between the lower end of the whip aerial and the take-up drum.

S. An aerial as claimed in claim 2, in which the nut member has a projection that engages with a slot in the inner surface of the wall of the housing so that the nut member slides relative to the housing when the inner member is rotated.

6. An aerial as claimed in claim 2, wherein the end of the coil adjacent the whip is connected to the whip through a rotatable electrical connection comprising a slip ring and sliding contact.

7. A centre-loaded tunable whip aerial, comprising a exible housing of insulating material forming the base section of the aerial, a flexible metal whip constituting a radiating member and secured to the upper end of said housing, a wire coil enclosed by the housing located towards the upper end 0f the housing and having one end electrically connected to said whip, a rotatable member about which said coil is wound, a nut member slidable relative to said housing and translationally movable on said rotatable member, an aperture in said nut member through which passes said Wire to provide a portion extending below said coil through the remainder of the housing to form a further radiating member, and means for adjusting the inductance value of said coil by moving the nut member on the rotatable member to alter the number of turns on the coil and thereby to effect tuning of the aerial.

8. A centre-loaded tunable whip aerial, comprising a flexible housing of insulating material forming the base section of the aerial, a flexible metal whip constituting a radiating member and rigidly secured to the upper end of said housing, a coil comprising a conductor embedded in the wall of the housing and having its upper end electrically connected to said whip, a further radiating member connected to the lower end of said coil and constituted entirely by a portion of the conductor embedded in the wall of the housing and extending below said coil and adjusting means located in said housing and operable remotely from said aerial for adjusting the inductance value of said coil so as to effect tuning of the aerial, said adjusting means comprising a core having a ferromagnetic portion, a non-conducting non-magnetic portion, and a conducting non-magnetic portion and remotely operable means for varying the position of the core relative to the coil.

9. An aerial as claimed in claim 8, in which said core has a ferromagnetic portion, a non-conducting paramagnetic portion and a conducting paramagnetic portion.

10. An aerial as claimed in claim 8, in which said core has a ferromagnetic portion, a non-conducting diamagnetic portion, and a conducting diamagnetic portion.

11. An aerial as claimed in claim 8, in which the movement of the core is remotely controlled by means of a cable, and a spring is located within the housing and urges the core in the opposite direction to the pull exerted by the cable.

12. An aerial as claimed in claim 8, in which the tuning core comprises a ferrite core portion composed of a plurality of separate units of ferrite material, a portion of insulating material, and a portion comprising a plurality of metal segments separated by means of spacers of insulating material, the various parts of the core being located around a central ilexible rod of insulating material which is anchored to two end pieces located at opposite ends of the core.

13. A centre-loaded tunable whip aerial, comprising a llexible thousing of insulating material forming the base section of the aerial, a flexible metal whip constituting a radiating member rigidly secured to the upper end of said housing, a coil comprising a conductor embedded in the wall of the housing and having its upper end electrically connected to said whip and its lower end connected to a further radiating member entirely embeded in the wall of the housing and extending below said coil and adjusting means located in said housing and operable remotely from said aerial for adjusting the inductance value of said coil so as to effect tuning of the aerial, said adjusting means comprising a core, having a ferromagnetic portion, a non-conducting non-magnetic portion and a conducting non-magnetic portion, spring means urging the core in one direction and a remotely operable cable for moving the core against the action of the spring means.

References Cited by the Examiner UNITED STATES PATENTS 2,232,693 2/1941 Dow 343-861 2,875,443 2/ 1959 Kandoian 343-749 2,894,260 7/1959 Ellis 343-861 2,931,034 3/1960 Harrison et al. 343-750 3,085,215 4/1963 Shepherd 343-750 3,104,394 9/1963 Yokoyama 343-750 HERMAN KARL SAALBACH, Primary Examiner. 

1. A CENTRE-LOADED TUNABLE WHIP AERIAL, COMPRISING A FLEXIBLE HOUSING OF INSULATING MATERIAL FORMING THE BASE SECTION OF THE AERIAL, A FLEXIBLE METAL WHIP CONSTITUTING A RADIATING MEMBER AND RIGIDLY SECURED TO THE UPPER END OF SAID HOUSING, A COIL ENCLOSED BY THE HOUSING LOCATED AWAY FROM THE LOWER END OF THE HOUSING AND HAVING ITS UPPER END ELECTRICALLY CONNECTED TO SAID WHIP, A FURTHER RADIATING MEMBER CONNECTED TO THE LOWER END OF SAID COIL, SAID FURTHER RADIATING MEMBER BEING ENTIRELY ENCLOSED BY THE 